1. Field of the Invention
The present invention relates to a flash unit, and more particularly to an inexpensive compact flash unit for a lens-fitted photographic film package, especially for a panoramic lens-fitted photographic film package.
2. Related Art
Lens-fitted photographic film packages for panoramic photography (hereinafter referred to as panoramic film packages) are known, for example, from U.S. patent application Ser. No. 07/667,758, which are a single-use throwaway camera pre-loaded with photographic film. Such panoramic film packages make it possible to take panoramic pictures whenever desired without buying or carrying an expensive and heavy camera. A panoramic film package uses a wide angle lens system having a short focal length of about 25 mm as a taking lens, and the exposed area of the film is defined by a horizontally extended frame 12.times.36 mm in size. Upon printing, the 12.times.36 mm picture frame is enlarged at a magnification twice the standard magnification for a standard 24.times.36 mm picture frame of 35 mm film. As a result, a print twice as long as a standard size print is provided.
Because of such a large print magnification, it is required to minimize the blur of the original images. For this reason, a panoramic film package presently marketed by Fuji Photo Film Co. Ltd. is provided with a pair of grips disposed on both horizontal sides of the taking lens, for surely and stably holding the panoramic film package. The grips also prevent the fingers from entering the wide angle field for panoramic photography which is defined by the angle of view of the taking lens.
The wide angle lens system is composed of two lenses. Because the principal point of the lens system lies between these lenses, an aperture stop member for defining the aperture size (the size of exposure opening) and a shutter mechanism for opening and closing the exposure opening are also disposed between these lenses.
The shutter mechanism includes a V-shaped shutter blade which is pivotal about an axis disposed at one end of the V-shape, whereas the other end of the V-shape opens and closes the exposure opening upon pivoting. The shutter mechanism further includes an actuating lever and a connecting lever. One end of the connecting lever is in the path of the actuating lever, and the other end is engaged with the elbow of the V-shaped shutter blade. When the actuating lever is moved, the movement is transmitted to the shutter blade through the connecting lever, and the shutter blade is caused to pivot in a direction perpendicular to the optical axis of the taking lens, thereby opening and closing the exposure opening. Since the connecting lever partly overlaps the shutter blade, the shutter blade is prevented from oscillating in the optical axis direction.
The Fuji panoramic film package is principally for use in bright outdoor light. Therefore, it is impossible to take properly exposed pictures under low light, such as indoors. However, it is desirable to incorporate a flash unit in the panoramic film package, so as to take pictures under low light, for example for photographing a number of people standing side by side in a gathering.
Because the panoramic film package is a kind of disposable camera, it is necessary to minimize the cost of the flash unit, as well as the cost of the other parts of the panoramic film package. For this reason, it is preferable to use in the panoramic film package a simple flash unit as used in Fuji standard-type film packages for standard photography, such as disclosed in U.S. Pat. Nos. 4,896,178 and 5,003,330.
However, because the Fuji flash unit needs a charge switch, and a charge switch operation member is disposed on the front wall of the film package, it becomes necessary for incorporating the flash unit in the panoramic film package, to provide a charge switch operation member in addition to the grips on the front wall of the panoramic film package. If the charge switch is formed separately from the grips, the photographer must remove the fingers from one of the grips in order to charge the flash unit. This is inconvenient, and may reduce the stability of holding the film package, and so may cause a blur.
Such a simple flash unit also has a simple synchro-flash switch mechanism, wherein the synchro-flash switch contact is formed as a pair of resilient contact segments extending parallel to each other. A shutter blade disposed behind a single element taking lens pivots about an axis so as to open and close an exposure opening. The first contact segment is disposed in the path of the shutter blade, such that the shutter blade depresses the first contact segment upon fully opening the exposure opening. Thereby, the contact segments are brought into contact with each other, generating a synchro-flash signal.
However, it is difficult to dispose such contact segments in the path of the shutter blade of the panoramic film package. This is because the shutter mechanism of the panoramic film package is composed of a connecting lever and a shutter blade, and because these elements are disposed between two lenses, as described above. In addition to such a complicated construction, the shutter blade of the panoramic film package cannot be projected sufficiently from the lens holding portion. Consequently, it is necessary to change the taking lens system or the shutter mechanism of the panoramic film package from the construction of the Fuji panoramic film package in order to enable depression of the contact segment by the shutter blade. This increases the cost of the panoramic film package.
Moreover, because the simple flash unit is designed for standard-type film packages, of which the focal length is 35 mm and the exposure frame is 24.times.36 mm in size, the illuminating field of the flash unit is adapted to cover a photographic field defined by this focal length and this frame size, that is, a field defined by a horizontal angle of view of about 53.degree., and a vertical angle of view of 38.degree..
However, the horizontal and vertical view angles of the above-described panoramic film package are 75.degree. and 24.degree., respectively. Obviously, the horizontal illuminating angle of the flash unit cannot cover the horizontal view angle of the panoramic film package. Therefore, if such a flash unit were used in the panoramic film package, both side areas of the panoramic photograph taken with flash would be under-exposed. On the other hand, because the vertical illuminating angle of the standard flash unit is too large relative to the vertical view angle of the panoramic: film package, the flash unit would illuminate uselessly the area beyond the vertical view angle of the panoramic film package.